In a battery pack including a plurality of stacked cells, the output voltage can be increased by interconnecting the cells in series, the output current can be increased by interconnecting the cells in parallel. Therefore, the battery pack having this structure is used as a power source of a large output and a large capacity, for example, as a power source device for a vehicle. In the battery pack having this structure, a cell stacked body is grasped with end plates at its opposite ends and is firmly fixed. The end plates fixed in a state where the cells are pressurized require a robust structure. When the cells swell due to the charge and discharge, a high pressure acts on the end plates. The end plates not only must have a high rigidity, but also must be lightweight without being thickened. That is because heavy end plates increase the weight of the battery pack and thick end plates increase the size of the battery pack. In the battery pack, the charge/discharge capacity per unit weight and unit volume can be increased by decreasing the weight and thickness of the end plates. This characteristic is extremely important in all applications of the battery pack. For example, this characteristic in a battery pack mounted in a vehicle improves the fuel consumption of the vehicle, and allows the battery pack to be mounted in a small installation space.
An end plate is produced by molding a resin or by molding or cutting a metal. However, a resin-made end plate can be made lightweight but cannot obtain a high rigidity. Disadvantageously, a metal-made end plate can obtain a high rigidity but cannot be made lightweight.
Patent Literature 1 discloses an end plate formed of a metal plate and a resin plate.